1. Technical Field
The present invention relates in general to electrical submersible pump assemblies and, in particular, to an improved system, method, and apparatus for controlling the flow rate of an electrical submersible pump based on measurements of at least one physical property of the fluid being produced.
2. Description of the Related Art
The separation of gases and liquids carried out in a well bore is common. In addition, separation of gasses and liquids at the seabed as part of a subsea oilfield exploitation is becoming increasingly common. Separating the gas and using a high head centrifugal pump to pump the liquids vastly improves the project economics (e.g., asset net present value and recovery factor). The separation of the gas from the liquid also results in improved flow assurance. Moreover, pumping fluids that contain excessive amounts of gas can cause gas lock in a pump or can cause a pump to overheat and fail prematurely.
Currently, in a well bore, the accepted method of controlling the gas-liquid interface level is to manually control the amount of fluid produced by a down hole electric submersible pump (ESP). Generally, the ESP is installed and the production rate is set. If the pump encounters a gas lock condition, it is shut down to allow the well to recover, restarted and a new lower production rate is manually set. This is continued until the ESP is operating in a continuous and stable manner. Conversely, if the pump does not gas lock when the ESP is first installed and is operating in a stable manner, the production rate is manually increased in steps until a gas lock condition occurs. After recovery, the production rate is then reduced to the point of the last stable operation. The object is to produce the maximum fluid available from the well with the pumping equipment.
In surface or subsea canned boosters, the methods for measuring and controlling the gas-liquid interface level is insufficient. In one type of installation, pressure transducers are used to infer, rather than measure, the interface level based on the pressures of the fluids at given elevations in the can or vessel. This method requires a significant difference in height between the transducers to achieve the required resolution in a high pressure vessel. Consequently, oversized and more expensive pressure vessels are used to enable this method. While this solution is satisfactory for some applications, an improved method to monitor fluid parameters and optimize pump performance would be desirable.